Apparatus for converting light beams

ABSTRACT

Optical devices for reforming optical beam and, hence, changing its size-divergence products along two directions perpendicular to beam propagating direction is disclosed. In one approach 90° roof reflector array is employed while in another approach 45° roof reflector array is employed. A simple reflection on the roof reflector array reforms optical beam and enables the adjustment of size-divergence product and, hence, provides the possibility of achieving symmetric beam. The other applications of the devices are beam switch beam equalizer. The devices are of great significance for diode laser and diode laser array.

TECHNICAL FIELD

This invention relates generally to optical systems and, moreparticularly, to a beam reforming apparatus for light beam or light beamarray to achieve symmetric size-divergence product along two orthogonaldirections perpendicular to propagating direction and to switch,equalize light power between two directions orthogonal to each other.

BACKGROUND

It is well-known that due to optical invariance, the size-divergenceproduct (SDP), or Lagrange invariant, of a light beam is constantthroughout an optical system.

The large difference in beam quality of edge emitting diode laser alonglateral direction, the direction parallel to its PN junction or quantumwell plane, and transverse directions, the direction perpendicular to PNjunction or quantum well plane, results in difficulty when it is desiredto focus the diode beam into a spot with symmetric size and divergenceor to coupled the diode beam into a fiber. For a typical diode laseremitter, the lateral dimension is d_(s)=159 μm, the transverse dimensionis d_(f)=1 μm and the divergent angle along lateral direction (slowaxis) is θ_(s)=12°, the divergent angle along transverse direction (fastaxis) is θ_(f)=40°. The size divergence product along lateral directionis SDPs=d_(s) sin (θ_(s)/2)=16.62, and size-divergence product alongtransverse direction is SDP_(f)=d_(f) sin (θ_(f)/2)=0.34. The ratio ofsize-divergence product along the two directions isR=SDP_(s)/SDP_(f)=d_(s) sin (θ_(s)/2)/d_(f) sin (θ_(f)/2)=17.36/0.34=49.The great R indicates the asymmetric property of the light beam and nooptical system can focus the beam into a symmetric spot where both itssize and divergence angle, or NA, along slow axis and fast axis areequal to each other. The R can be even greater when a wider emitter or awhole diode laser bar which consists of a linear array of emitters alongtheir slow axis is considered.

There are a number of beam shaping techniques to produce round beam spotfrom line-like emission of edge emitting diode laser at certaindistance. However, the inherent SDP difference is still an obstacle forsome of its applications.

To overcome the difficulty cause by the inherent asymmetric property ofedge emitting diode laser, techniques have been developed whichsuccessfully reformed the laser beam, such as U.S. Pat. No. 5,168,401,No. 5,592,333, No. 6,240,116 and No. 4,763,975.

This invention adds two more approaches in the beam reforming efforts toreforming line-like beam including the beam from edge emitting diodelaser and beams from edge emitting diode laser array by a simplereflection on a roof reflector array. The devices are wavelengthindependent. In addition, the invention provides other applications, forexample, switch and beam equalizer.

SUMMARY OF THE INVENTION

This invention is to manipulate light beam or beam array to change theirSDPs along lateral and transverse directions, or to switch the positionand propagation direction of light beam or beam array.

Following approach is employed for this purpose.

A beam manipulation device which consists of a roof reflector or a roofreflector array with following features.

The roof reflector consists of two mirror, their intersect line is ridgeof the roof reflector; the dihedral angle is the integer times of 45°,but not greater than 90°.

All of the roof reflectors are aligned along the lateral direction ofthe incoming light beam or beam array with their opening towards theincoming beam or beam array and their ridges parallel to the transversedirection of the beam or beam array; all of the roof reflectors or roofreflector array are integrated on a plate which can rotate arbitrarily;

In one embodiment of the invention, the dihedral angle is 45°.

In other embodiment of the invention, the dihedral angle is 90° and theridges of the roof reflectors or roof reflector array are rotated aroundthe propagating direction of the light beam or beam array by 45°.

For beam array, the opening of each roof reflector is equal to or largerthan the width of each beam at the roof reflector. For single beam, theroof reflector opening can be smaller than, equal to or larger than thebeam width at reflector.

The device described above can either reform a light beam like the beamor beam array from edge emitting diode laser into a new beam array withequal SDP along lateral and transverse directions or redirect the lightbeam or beam array into two directions orthogonal to each other withadjustable strength.

DESCRIPTION OF DRAWINGS

FIG. 1 presents a 90° roof reflector consisting of two mirrorsperpendicular to each other, the intersection line of the two mirrors isthe ridge.

FIG. 2 presents a tilt about Z-axis by −45° on the 90° roof reflector inFIG. 1, the tilted 90° roof reflector is reflector 5.

FIG. 3 presents further tilting on the 90° roof reflector 5 presented inFIG. 2: a tilt about X-axis by −45°. The tilted roof reflector is 90°roof reflector 8.

FIG. 4 presents one of the embodiments of this invention to tailor beamsize-divergence product (SDP) at its lateral and transverse directions.

FIG. 5 presents another embodiment of this invention for a wide emitter.90° roof reflector array 24 is built and placed in the same way as array17 in FIG. 4 except that there is no flat strip between adjacentreflectors.

FIG. 6 presents another roof reflector which is a 45° roof reflectorconsisting of two mirrors 25 and 26 with 45° dihedral angle.

FIG. 7 presents what is going to happen when a thin beam 28 comes to 45°roof reflector.

FIG. 8 presents a beam 31 originated in X-Z plane from the negative sideof X-axis propagating upward to the 45° roof reflector with directionalcosine (0, −1/√{square root over (2)}, 1/√{square root over (2)}).

FIG. 9 presents a thin beam 33 originated in X-Z plane from the positiveside of X-axis propagating upward to the 45° roof reflector withdirectional cosine is (0, −1/√{square root over (2)}, 1/√{square rootover (2)}).

FIG. 10 presents an embodiment of this invention where beams propagateupward to a 45° roof reflector array and get reflected so that beamconfiguration, as well as SDP along lateral and transverse directions,is changed.

FIG. 11 presents an embodiment of this invention where a group of raysoriginated from X-Z plane with different x positions are coming upwardto a 45° roof reflector and get reflected so that the directions andpositions of the reflected rays are related to their original positions.

DETAILED DESCRIPTION OF THE INVENTION

The optical principle of this invention are depicted in FIG. 1 throughFIG. 3 and FIG. 6 through FIG. 9. The roof reflector consists of twomirrors, their intersect line is the ridge, their dihedral angle is 90°or 45° called 90° roof reflector or 45° roof reflector, respectively.

In FIG. 1, the ridge of the 90° reflector is placed on Y-axis and Y-Zplane is its planar bisector. Ray 1 at x=g in X-Z plane propagatesparallel to Z-axis towards the roof reflector; it is reflected back inreverse direction and the reflected ray 2 will be at x=−g. If a thinbeam 3 in X-Z plane, instead of ray 1, with its width from −g to gincidents on the roof reflector, the reflected beam 4 will be comingback in X-Z plane in reverse direction of beam 3. The beam orientationwill be rotated about Z-axis by 180°, as the small circles near beam 3and 4 indicated.

Then the 90° reflector is tilted about Z-axis by −45° becoming reflector5 (FIG. 2). The thin light beam 6 in X-Z plane propagating to thereflector along Z-axis with its lateral direction being parallel toX-axis and transverse direction being parallel to Y-axis is reflected;the reflected beam 7 propagates along −Z-axis in Y-Z plane. However, dueto the tilting on 90° roof reflector, the orientation of reflected beam7 has been rotated about Z-axis by 90°, as the small circle besides beam6 and beam 7 indicated.

In order alter the propagate direction of the reflected beam 7, the 90°roof reflector is further tilted about X-axis by −45° becoming roofreflector 8 in FIG. 3, the lateral direction of incoming beam 9 is alongX-axis. The reflected beam becomes 10. The reflected beam 10 comes outin Y-Z plane with directional cosine (−1/√{square root over (2)},−1/√{square root over (2)}, 0), and its lateral direction is alignedwith negative Z-axis, (the small circles near the two beams indicatebeam orientation). In other words, two significant changes in thereflected light beam 10 have happened: beam propagating direction ischanged from being parallel to Z-axis with directional cosine (0, 0, 1)to being perpendicular to Z-axis with directional cosine (−1/√{squareroot over (2)}, −1/√{square root over (2)}, 0) and beam orientation ischanged from being perpendicular to Z-axis to being parallel to negativeZ-axis. These changes caused by the 90° roof reflector 8 are importantin its application.

One of the embodiments of this invention is a beam reforming devicewhere 90° roof reflector is used (FIG. 4). A diode laser bar 11 ismounted on its substrate 12. On the bar, there are emitters distributedin a line along emitter lateral direction (X direction), their emissionalong emitter transverse direction (Y direction) is, for the purpose ofclarity, collimated by micro lens 13 but their divergence along lateraldirection is not collimated. The transversely collimated beams (14, 15,16) are propagating along emitter longitudinal direction (Z direction)and come to plate 17 where an array of 90° roof reflectors (18, 19, 20)in the configuration described in FIG. 3 is placed. The reflector widtht is equal or larger than beam width at reflector, and reflector periodw is the same as the emitter period w on diode laser bar 11. Thereflected beams will be propagating with directional cosine (−1/√{squareroot over (2)}, −1/√{square root over (2)}, 0) which is perpendicular toZ-axis. The beam configuration, thus, has been rearranged: light beams(14, 15, 16) lined along their lateral direction with period w turn intolight beams (21, 22, 23) stacked along beam transverse direction withperiod w. This rearrangement provides possibility to tailor beamsize-divergence product (SDP) along its lateral and transversedirections.

Another embodiment of this invention is for wide emitter (FIG. 5). 90°roof reflector array 24 of totally n reflectors is built and placed inthe same way as array 17 in FIG. 4 except that there is no flat stripbetween adjacent reflectors. Beam 25 of width D from the wide emitter isreflected by 90° roof reflector array 24. After reflection, the widebeam D is chopped into n narrow beams stacked along beam lateraldirection with period of d. where d=D/n and n should be integer.

As discussed in U.S. Pat. No. 5,168,401, the product of SDP ratio R forincoming beam times and SDP ratio R′ for reflected beam equals to n²,i.e. RR′=n². Thus, by properly choosing n, beam SDP ratio R′ can beadjusted. If, for example, R′=1 is needed, then simply build said 90°roof reflector array 24 with n=√{square root over (R)}. In our case, n=7is a good design for R=49. Again, for the purpose of clarity, beam D iscollimated along its transverse direction but not collimated along itslateral direction. In real case, beam collimating before 90° roofreflector array 24 is not necessary.

The array of 90° roof reflectors can be arbitrarily rotated aroundX-axis and the direction of reflected beam will be changingcorrespondingly, but the product of SDP ratio R for incoming beam timesand SDP ratio R′ for reflected beam will never be changing.

A 45° roof reflector consisting of two mirrors 25 and 26 with 45° roofangle (FIG. 6). Ray 27 is parallel to its angular bisector Z-axis. Whenthe ray comes to mirror 25, it is reflected to mirror 26. After beingreflected from mirror 26, the ray will propagate in a direction parallelto X-axis. The dashed lines perpendicular to mirror 25 and 26 are theirnormal.

When a thin beam 28, instead of a ray 27, comes to the 45° roofreflector (FIG. 7), the beam will be reflected by mirror 29 first andthen reflected by mirror 30. After the two reflections, the beam willpropagate in parallel to X-axis, its lateral direction will be turnedabout Y-axis by −90° as what the small circle indicated.

The 45° roof reflector configuration provides a number of applications.For example, if the light beam propagates towards 45° roof reflectorupwardly with directional cosine (0, −1/√{square root over (2)},1/√{square root over (2)}) , as beam 31 in FIG. 8 does, the reflectedbeam 32 will propagate with directional cosine (−1/√{square root over(2)}, −1/√{square root over (2)}, 0) which is perpendicular to Z-axis.If the position of beam 31 in FIG. 8 is shifted from negative on X-axisto positive on X-axis, as beam 33 in FIG. 9 does, the reflected beam 34is still perpendicular to Z-axis but the directional cosine becomes(1/√{square root over (2)}, −1/√{square root over (2)}, 0) which isorthogonal to beam 32 in FIG. 8.

An array of 45° roof reflectors can also be employed to reform a lightbeam array. In one of the embodiments of this invention (FIG. 10), beamsfrom emitters on diode laser bar 11 are collimated by lens 13 andpropagate upward to a 45° roof reflector array 35, the upward angle is45° or other angle as long as the beams can be reflected out of the 45°roof reflector array 35. The period of 45° roof reflectors in the array35 is r which is also the period of emitters on diode bar 11. The beamwidth at 45° roof reflector array 35 is less than half of the reflectorwidth q, so that beams shine on only one of the two mirrors of areflector. It is seen again that the incoming beams aligned along beamlateral direction with period r turn out to be stacked along transversedirection with period r after being reflected. This change, once again,provides a beam reforming approach to tailor SDP along lateral andtransverse directions.

Another embodiment of this invention is beam equalizer (FIG. 11). Sixrays, or beams, originated from X-Z plane with x=a, b, c d, e, f,respectively, are coming upward to a 45° roof reflector. Their upwardangle is 45° or other angle as long as the beams can be reflected out ofthe 45° roof reflector array. Three of them originated from the negativeside of X-axis, i.e. x=a, b, c, will be reflected and propagating withdirectional cosine (−1/√{square root over (2)}, −1/√{square root over(2)}, 0), perpendicular to Z-axis. In addition, they will be alignedalong Z-axis as the dashed line indicated, and their coordinates onZ-axis have the same values as their coordinates on X-axis, i.e. Z=a, b,c, respectively. Similarly, the other three originated from the positiveside of X-axis, i.e. x=d, e, f, will be reflected and propagating withdirectional cosine (1/√{square root over (2)}, −1/√{square root over(2)}, 0), perpendicular to Z-axis, and aligned along Z-axis as thedashed line indicated. Their coordinates on Z-axis have the same valuesas their coordinates on X-axis but are all negative, i.e. Z=d −e, −f,respectively. Thus, the incoming beam representing by the six rays, orbeams, has been divided into two groups of reflected beams propagatingorthogonal to each other. Since the light power in each group is thefunction of incoming beam position on X-axis, this is obviously a beampower equalizer. It is also obvious that, as a beam power equalizer, thebeam width at the reflector can be wider than the half of the reflectoropening q.

Moreover, the embodiment of this invention can also be a beam positionindicator and direction switch: when the intersect point of an incomingray on a mirror of the 45° roof reflector is moving along X-axis, thereflected ray is moving along Z-axis, which makes the 45° roof reflectorswitched a position transformer. However, in case that the intersectpoint of an incoming ray totally moves from one mirror to other mirror,the reflected beam switch from one direction to other direction and thetwo directions are orthogonal to each other. The 45° roof reflector, inthis case, functions as a switch. Similarly, if there is incoming rayarray, or beam array, the 45° roof reflector functions as Mx2 switchwhere M is the number of rays in the ray array, or the number of thebeams in the beam array.

The light beam in this patent can be either non-coherent or coherentsuch as beam from lasers including diode laser; it can be a wide beam oras narrow as a ray. The beam in this patent can be either collimated ornon-collimated. The beams in a beam array can be either identical ordifferent, i.e. the beam width and spacing between beams vary from beamto beam. For beam array with non-identical beams, the corresponding roofreflectors in the roof reflector array are non-identical, too, and eachindividual roof reflector has one-to-one accordance to the beam.However, the one-to-one correspondence between roof reflectors andemitters is not necessary; the total number of roofs in the roofreflector array can be set based the desired R and the total width ofthe beam array and divergence angles. The two adjacent roof reflectorscan touch to each other (FIG. 5 and FIG. 10), no flat strip in between(FIG. 4) depending on the need for reflection from the flat strip.

Given the detailed description on the functions of this patent, anyobvious modifications with no essential difference from the principle ofthis patent will constitute violation of patent rights.

1. An optical apparatus for reforming beams in a beam array, saidapparatus comprising: a plurality of light beams arranged to form aperiodic light beam array, said light beam array defining a lateraldirection (parallel to X-direction) along an array axis passing througha line of beams on said light beam array, a transverse direction(parallel to Y-direction) perpendicular to lateral direction and beampropagating direction (parallel to Z-direction), each of said light beamin said array being identical and characterized by d_(s), lateraldimension, d_(f), transverse dimensions, θ_(s), lateral divergenceangle, and θ_(f), transverse divergence angle, said light beam arraybeing characterized by N_(b), total number of said light beams, p_(b),said beam period along lateral direction, and w_(b), width of said lightbeam which is, in general, the function of propagating distance(Z-direction); and a plurality of roof reflectors arranged to form aperiodic roof reflector array, each said roof reflector in said arraybeing formed of two reflecting surfaces which intersect along ridge andform a dihedral angle Φ between them, each said ridge being parallel toeach other and oriented at a projected angle ψ_(x-y) from y-axis in x-yplane, a projected angle ψ_(y-z) from y-axis in y-z plane, said roofreflector array being characterized by N_(r), total number of said roofreflectors, p_(r) period of said reflector, and w_(r), width of saidroof reflector opening, and being placed in front of said light beamarray with the opening of roof reflectors towards said light beams, saidroof reflectors in said roof reflector array having at least aone-to-one correspondence with said light beams in said light beam array(p_(b)=p_(r)) to intercept incoming said light beams in said lightbeams, rotate them by reflecting them on its two reflecting surfaces,alter their propagating direction and, hence, change the configurationof said light beam array or beam SDP ratio R.
 2. The optical system ofclaim 1 wherein said light beams are coherent beams from lasersincluding diode laser emitters on diode laser bar propagating alonglongitudinal direction of diode laser cavity with beam properties andparameters from said diode laser emitters.
 3. The optical system ofclaim 2 wherein the said light beams from emitters on diode laser bar iscollimated.
 4. The optical system of claim 1 wherein the width of saidlight beam in said light beam array at corresponding said roof reflectorin said roof reflector array is equal to the width of the roof reflectoropening w_(r).
 5. The optical system of claim 1 wherein the width ofsaid light beam in said light beam array at corresponding said roofreflector in said roof reflector array is smaller than the width of theroof reflector w_(r).
 6. The optical system of claim 1 wherein saidlight beams in said light beam array are not identical in width but saidlight beam array is still periodic.
 7. The optical system of claim 6wherein said light beam array is not periodic.
 8. The optical system ofclaim 1 wherein said roof reflectors in said roof reflector array arenot in a one-to-one correspondence with said light beams in said lightbeam array but both said arrays are still periodic and reflector periodp_(r) is set according to the desired beam SDP ratio R.
 9. The opticalsystem of claim 8 wherein said beams in said light beam array are notidentical in width.
 10. The optical system of claim 9 wherein said lightbeam array is not periodic.
 11. The optical system of claim 8 whereinN_(b)=1 and N_(r)>1.
 12. The optical system of claim 1 whereinp_(r)>w_(r) and said roof reflector array has flat strips, which canreflect light, between two adjacent roof reflectors.
 13. The opticalsystem of claim 1 wherein ψ_(y-z) is any angle as long as said lightbeam array can be reflected out off said roof reflector array andfurther propagate.
 14. The optical system of claim 13 whereinψ_(x-y)=45° and Φ=90°.
 15. The optical system of claim 13 whereinψ_(x-y)=0° and Φ=45°.
 16. The optical system of claim 15 wherein theposition of said light beam array relative to said roof reflector arrayis adjustable along x-axis.
 17. The optical system of claim 16 whereinN_(b)=1 and N_(r)=1.